1,277 research outputs found

    Education and Contraceptive Choice: Conditional Logit and Structural Models

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    Orientation reversal of manifolds

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    We call a closed, connected, orientable manifold in one of the categories TOP, PL or DIFF chiral if it does not admit an orientation-reversing automorphism and amphicheiral otherwise. Moreover, we call a manifold strongly chiral if it does not admit a self-map of degree -1. We prove that there are strongly chiral, smooth manifolds in every oriented bordism class in every dimension greater than two. We also produce simply-connected, strongly chiral manifolds in every dimension greater than six. For every positive integer k, we exhibit lens spaces with an orientation-reversing self-diffeomorphism of order 2^k but no self-map of degree -1 of smaller order.Comment: This is the update to the final version. 22 page

    Changes in seagrass polychaete assemblages after invasion by Caulerpa racemosa var. cylindracea (Chlorophyta: Caulerpales): community structure, trophic guilds and taxonomic distinctness

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    A two-year study focusing on the associated polychaete assemblages revealed that the degradation of the Posidonia oceanica seagrass meadows, together with the colonisation of rhizomes by invasive Caulerpa racemosa in the Balearic Islands, have produced important changes in the ecosystem functioning, and have therefore affected the benthic faunal communities. The highest abundance and number of species occurred in C. racemosa from August to December. The species composition of the polychaete assemblage in C. racemosa is similar to that of P. oceanica but abundances of shared species differ between Caulerpa and Posidonia. Abundance, number of species and diversity were positively correlated with C. racemosa biomass. The spatial complexity provided by the network of C. racemosa fronds and stolons seemed to combine with that of the remaining seagrass mat to support a well developed polychaete assemblage. Although invaded meadows harboured significantly modified polychaete assemblages when compared with living P. oceanica meadows, the main impacts seem to be non-harmful (i.e. increased abundance and number of species) and mainly affect their seasonal patterns, which is a direct consequence of the corresponding biomass seasonality of C. racemosaPublicado

    Climate Change in New York State Updating the 2011 ClimAID Climate Risk Information Supplement to NYSERDA Report 11-18 (Responding to Climate Change in New York State)

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    In its 2013-2014 Fifth Assessment Report (AR5), the Intergovernmental Panel on Climate Change (IPCC) states that there is a greater than 95 percent chance that rising global average temperatures, observed since the mid-20th century, are primarily due to human activities. As had been predicted in the 1800s, the principal driver of climate change over the past century has been increasing levels of atmospheric greenhouse gases associated with fossil-fuel combustion, changing land-use practices, and other human activities. Atmospheric concentrations of the greenhouse gas carbon dioxide are now approximately 40 percent higher than in preindustrial times. Concentrations of other important greenhouse gases, including methane and nitrous oxide, have increased rapidly as well

    Characterization of chemical and bacterial concentrations in floor dust samples in southeast texas households

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    Indoor dust can be a major source of heavy metals, nutrients, and bacterial contamination in residential environments and may cause serious health problems. The goal of this research is to characterize chemical and bacterial contaminants of indoor, settled house dust in the Houston Metropolitan region. To achieve this, a total of 31 indoor dust samples were collected, along with household survey data, which were subsequently analyzed for elemental and bacterial concentrations. Microscopic and geospatial analysis was conducted to characterize and map potential hotspots of contamination. Interestingly Cd, Cr, Cu, Pb, and Zn concentrations of all 31 indoor dust samples were significantly enriched and exceeded soil background concentrations. Furthermore, As, Cd, Pb, and Zn concentrations in the dust samples were significantly correlated to the enteric bacterial load concentrations. Human health assessment revealed that cancer risk values via ingestion for Cd, Cr, and Ni were greater than the acceptable range. Of our 31 dust sample isolates, three Gram-negative and 16 Gram-positive pathogenic bacteria were identified, capable of causing a wide range of dis-eases. Our results demonstrate that both chemical and bacterial characterization of indoor dust coupled with spatial mapping is essential to assess and monitor human and ecological health risks

    The species-area relationship and evolution

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    Models relating to the Species-Area curve are usually defined at the species level, and concerned only with ecological timescales. We examine an individual-based model of co-evolution on a spatial lattice based on the Tangled Nature model, and show that reproduction, mutation and dispersion by diffusion in an interacting system produces power-law Species-Area Relations as observed in ecological measurements at medium scales. We find that co-evolutionary habitats form, allowing high diversity levels in a spatially homogenous system, and these are maintained for exponentially increasing time when increasing system size.Comment: 21 pages, 5 figures. This is the final, accepted draf

    Climate Hazard Assessment for Stakeholder Adaptation Planning in New York City

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    This paper describes a time-sensitive approach to climate change projections, developed as part of New York City's climate change adaptation process, that has provided decision support to stakeholders from 40 agencies, regional planning associations, and private companies. The approach optimizes production of projections given constraints faced by decision makers as they incorporate climate change into long-term planning and policy. New York City stakeholders, who are well-versed in risk management, helped pre-select the climate variables most likely to impact urban infrastructure, and requested a projection range rather than a single 'most likely' outcome. The climate projections approach is transferable to other regions and consistent with broader efforts to provide climate services, including impact, vulnerability, and adaptation information. The approach uses 16 Global Climate Models (GCMs) and three emissions scenarios to calculate monthly change factors based on 30-year average future time slices relative to a 30- year model baseline. Projecting these model mean changes onto observed station data for New York City yields dramatic changes in the frequency of extreme events such as coastal flooding and dangerous heat events. Based on these methods, the current 1-in-10 year coastal flood is projected to occur more than once every 3 years by the end of the century, and heat events are projected to approximately triple in frequency. These frequency changes are of sufficient magnitude to merit consideration in long-term adaptation planning, even though the precise changes in extreme event frequency are highly uncertai

    The Valley-of-Death: Reciprocal sign epistasis constrains adaptive trajectories in a constant, nutrient limiting environment

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    The fitness landscape is a powerful metaphor for describing the relationship between genotype and phenotype for a population under selection. However, empirical data as to the topography of fitness landscapes are limited, owing to difficulties in measuring fitness for large numbers of genotypes under any condition. We previously reported a case of reciprocal sign epistasis (RSE), where two mutations individually increased yeast fitness in a glucose-limited environment, but reduced fitness when combined, suggesting the existence of two peaks on the fitness landscape. We sought to determine whether a ridge connected these peaks so that populations founded by one mutant could reach the peak created by the other, avoiding the low-fitness Valley-of-Death between them. Sequencing clones after 250 generations of further evolution provided no evidence for such a ridge, but did reveal many presumptive beneficial mutations, adding to a growing body of evidence that clonal interference pervades evolving microbial populations

    Plasma accelerator-based ultrabright x-ray beams from ultrabright electron beams

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    We provide a pathway to compact ultrabright light sources, based on ultrabright, high energy electron beams emerging from a combination of plasma Wakefield acceleration and plasma photocathodes. While plasma acceleration is known to produce accelerating fields three or four orders of magnitude larger than conventional accelerators, the plasma photocathode allows production of electron beams three or four orders of magnitude brighter than conventional, and thus is suitable to unleash the full potential of plasma accelerators. In particular, this is the case for various types of light sources, which profit enormously from an increased electron beam brightness. Building on the recent first experimental demonstration of the plasma photocathode, in this work we discuss the prospects of plasma photocathodes for key photon source approaches such as x-ray free-electron lasers, betatron radiation, ion-channel lasers and inverse Compton scattering
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